1. Field of the Invention
The present invention relates to a sealed housing of a device to be installed in a motor vehicle as well as to a method of producing the same.
2. Description of the Related Art
Sealed housings in motor vehicles may accommodate e.g. control devices which should be hermetically sealed in the housing in a dustproof manner. These devices are especially electronic control devices, which may be sensitive to contamination and environmental influences as well as humid air. A sealed housing according to the present invention may, however, also be a housing in which a medium is conducted and/or accommodated.
Such a sealed housing is known e.g. from DE 196 42 442 A1. This publication discloses a sealed housing of an electric heating device comprising a housing lower part and a housing cover, which abuts on the housing lower part via an intermediate sealing element.
EP 2 440 004 A1, which is owned by the present applicant, also discloses a sealed housing of an electric heating device. This publication discloses in its FIG. 7 two identically configured housing parts which are interconnected via an intermediate sealing layer and which each define a circulation chamber for a fluid to be heated.
This known prior art as well as the prior art according to DE 196 42 442 A1 disclose, in essence, a water heater, i.e. a heater, accommodating a fluid medium in the housing lower part. The housing lower part is closed by the housing cover, the sealing element preventing leakage at the location where the housing lower part and the housing cover are joined.
In the case of the housings to be sealed in the above-mentioned prior art examples, the housing cover is screw-fastened to the housing lower part. In the automotive industry, screw connections must nowadays satisfy special demands for reasons of quality control. Normally, the torque is measured during tightening of the screw connection, so that possible complaints can be traced later on. In particular when the components in question are safety relevant, the torque measured during screw-fastening of the housing is additionally documented and archived.
Screw connections are additionally disadvantageous insofar as they may become loose due to the vibrations in the vehicle. The desired leakproofness of the sealed housing will thus get lost. In the case of a water heater, the medium conducted in the heating circuit may escape through the leak, and this may result in excessively high temperatures in the system and cause substantial damage to the system in its entirety.
It is indeed possible to join the housing cover and the housing lower part by welding or by an adhesive, but this kind of connection between the two housing parts prevents easy opening of the housing for the purpose of revision or repair. Therefore, the sealed housing can normally be disposed of only together with the device contained in the housing. In addition, only housing parts consisting of identical substances can be joined by welding.
Sometimes, it is necessary to configure housings such that weight is saved, in which case plastic will be the obvious material to use. The housing is, however, arranged close to temperature sources and/or may surround and/or contain these sources of heat, and this prevents—depending on the actually occurring temperatures—the use of plastic, at least for certain parts of the housing. Producing the housing of identical substances is thus not always possible.
Especially in media-carrying housings, substantial tensions may occur on the joining area due to the operating pressure of the respective medium, and a welded joint, in particular a welded joint of plastic materials, will not always be able to reliably resist these tensions. Hence, a welded joint between the housing parts to be joined entails the risk that the housing will fail when subjected to an internal pressure of the medium accommodated and sealed in the sealed housing.